The present invention relates to a semiconductor light-emitting device for transmission use (in particular, for IEEE 1394), display use and the like and a method for fabricating the device.
In recent years, semiconductor light-emitting devices are broadly used for optical communications and display panels. It is important for the semiconductor light-emitting devices for the above uses to have a high light emission efficiency, and it is further important for semiconductor devices for optical communications to have a high speed of response. Such devices have been actively developed lately.
The normal plane emission type LED""s (light-emitting diodes) have an insufficient high-speed response, which is limited to about 100 Mbps to 200 Mbps. Accordingly, there is developed a semiconductor light-emitting device called the resonant-cavity type LED. This resonant-cavity type LED is a semiconductor light-emitting device that achieves a high-speed response and high efficiency by controlling the natural emission light with a light-emitting layer placed in a belly position of a standing wave generated by a resonator formed of two mirrors (Japanese Patent Publication No. HEI 10-2744503, U.S. Pat. No. 5,226,053).
In particular, POF (plastic optical fiber) has lately started being utilized for communications in a relatively short range, and there has been developed a resonant-cavity type LED having a light-emitting layer made of an AlGaInP based semiconductor material capable of emitting with high efficiency light at a wavelength of 650 nm around which the POF has a small loss (High Brightness Visible Resonant Cavity Light Emitting Diode: IEEE PHOTONICS TECHNOLOGY LETTERS Vol. 10, No. 12, DECEMBER 1998).
However, the aforementioned conventional resonant-cavity type LED has the problems as follows. In detail, the conventional resonant-cavity type LED has characteristics such that a resonant wavelength xcex1 in the perpendicular direction and a resonant wavelength xcex2 in a slanting direction have a magnitude relation of xcex1 greater than xcex2 and a peak wavelength is varied depending on the angle of radiation from the LED chip. Normally, this radiation angle dependency is about 0.2 nm/deg to 0.3 nm/deg. This causes a problem that the color is varied depending on the angle of view when the LED chip is used for display.
When using the aforementioned LED chip for communications or as a light source for communications by means of, for example, a plastic fiber, an LED chip fabricated so as to have a peak at the wavelength of 650 nm at which the plastic fiber has a small loss in the perpendicular direction cannot be used in an optical system that utilizes the emission light in a slanting direction since the peak wavelength becomes shorter than 650 nm.
Accordingly, the object of the present invention is to provide a semiconductor light-emitting device whose emission light wavelength has a small radiation angle dependency and a method for fabricating the device.
In order to achieve the above object, there is provided a semiconductor light-emitting device having a resonator constructed of a pair of multi-layer reflection films formed with interposition of a specified interval on a GaAs substrate and a light-emitting layer formed in a belly position of a standing wave in the resonator, the device comprising:
a semiconductor layer which has one or more layers and an uppermost layer whose surface is roughened, the semiconductor layer being formed on the multi-layer reflection film located on the opposite side of the GaAs substrate with respect to the light-emitting layer.
According to the above-mentioned construction, the surface of the semiconductor light-emitting device is roughened. Therefore, as shown in FIG. 7A, light emitted from the light-emitting layer is diffused in various directions when emitted out of the surface of the semiconductor light-emitting device. As a result, the radiation angle dependency of the emission light wavelength is reduced.
In one embodiment of the present invention, the light-emitting layer is constructed of an AlyGazIn1xe2x88x92yxe2x88x92zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) layer comprised of a single layer or a plurality of layers.
According to the above-mentioned construction, the light-emitting layer is constructed of the AlyGazIn1xe2x88x92yxe2x88x92zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) layer comprised of a single layer or a plurality of layers. This enables the obtainment of emission light having a wavelength of 560 nm to 660 nm.
In one embodiment of the present invention, the multi-layer reflection film located on the GaAs substrate side with respect to the light-emitting layer is an AlxGa1xe2x88x92xAs (0xe2x89xa6xxe2x89xa61) layer, and the multi-layer reflection film located on the opposite side of the GaAs substrate with respect to the light-emitting layer is constructed of an AlyGazIn1xe2x88x92yxe2x88x92zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) layer.
According to the above-mentioned construction, the multi-layer reflection film located on the n-type GaAs substrate side with respect to the light-emitting layer is constructed of AlxGa1xe2x88x92xAs (0xe2x89xa6xxe2x89xa61). Therefore, a difference in coefficient of thermal expansion from the GaAs substrate is small. Therefore, dislocation due to a difference between a temperature before crystal growth and a temperature after crystal growth is hard to occur. This allows the number of layers of the multi-layer reflection film to be increased and allows a high reflectance to be easily obtained.
The multi-layer reflection film located on the opposite side of the GaAs substrate with respect to the light-emitting layer is formed of AlyGazIn1xe2x88x92yxe2x88x92zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61). Therefore, the layer that has lattice matching with the GaAs substrate includes Al at a maximum rate of about 25%, which is about one-half the rate of 50% in the case where the film is formed of AlxGa1xe2x88x92xAs (0xe2x89xa6xxe2x89xa61). Therefore, moisture resistance is remarkably improved.
Also, there is provided a method for fabricating a semiconductor light-emitting device having a resonator constructed of a pair of multi-layer reflection films formed with interposition of a specified interval on a GaAs substrate 1 and a light-emitting layer formed in a belly position of a standing wave in the resonator, the method comprising:
a process for forming a semiconductor layer having one or more layers on the multi-layer reflection film located on the opposite side of the GaAs substrate with respect to the light-emitting layer; and
a process for roughening a surface of an uppermost layer of the semiconductor layer.
According to the above-mentioned construction, the surface of the uppermost layer of the semiconductor layer formed on the resonator constructed of a pair of multi-layer reflection films is roughened. Therefore, light emitted from the light-emitting layer is diffused in various directions when emitted out of the surface of the semiconductor light-emitting device without reducing the reflectance of the multi-layer reflection films. As a result, the radiation angle dependency of the emission light wavelength is reduced.
In one embodiment of the present invention, the roughening of the surface of the uppermost layer of the semiconductor layer is performed by forming a light-difusing pattern by photolithography and etching.
According to the above-mentioned construction, the pattern that diffuses light is formed on the surface of the uppermost layer of the semiconductor layer by photolithography and etching. With this arrangement, a high-accuracy fine pattern is formed. Therefore, the degree of surface roughening is controlled so as to reduce the radiation angle dependency of the emission light wavelength.
In one embodiment of the present invention, the roughening of the surface of the uppermost layer of the semiconductor layer is performed by abrasion.
According to the above-mentioned construction, the surface of the uppermost layer of the semiconductor layer is roughened by abrasion. This obviates the need for the complicated photolithographic process as in the case where the light diffusing pattern is formed, and a semiconductor light-emitting device is fabricated by a simpler method.
In one embodiment of the present invention, the semiconductor layer is formed of AlyGazIn1xe2x88x92yxe2x88x92zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61), and
the roughening of the surface of the uppermost layer of the semiconductor layer is performed by scalding at least the semiconductor layer in hydrochloric acid.
According to the above-mentioned construction, the surface of the uppermost layer of the semiconductor layer is roughened by scalding the layer in hydrochloric acid. This obviates the need for the processes of sticking the entire wafer to another substrate, sheet or the like, holding the wafer and cleaning the wafer as in the case of the aforementioned abrasion. Therefore, a semiconductor light-emitting device is fabricated by a simpler method.
Also, there is provided a method for fabricating a semiconductor light-emitting device having a resonator constructed of a pair of multi-layer reflection films formed with interposition of a specified interval on a GaAs substrate 1 and a light-emitting layer formed in a belly position of a standing wave in the resonator, the method comprising:
a process for forming a semiconductor layer having one or more layers including an AlyGazIn1xe2x88x92yxe2x88x92zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) layer whose lattice constant differs from the GaAs substrate by 0.5% or more on a multi-layer reflection film located on the opposite side of the GaAs substrate with respect to the light-emitting layer, thereby roughening a surface of an uppermost layer of the semiconductor layer.
According to the above-mentioned construction, the surface of the semiconductor layer formed on the multi-layer reflection film located on the opposite side of the GaAs substrate with respect to the light-emitting layer is roughened by the lattice constant difference. Through this process, the surface of the semiconductor layer is roughened only by a sequence of the crystal growth process. This obviates the need for providing a process for separately performing the roughening after the crystal growth, and a semiconductor light-emitting device is fabricated by a further simplified method.